തണ്‌

wNT — ie ie ತ ರಷ್ಟ hea 4 record of bytes placed sequentially and the OS has the

‎functions. , : ^ WriteFile and SetFilePointer, and CloseHandle for creati fi‏ سس
ہی ‎ചു file, writing 8 ile and setting the file pointer from the present to 4 new location.‏
‎ப Unix has open ( ), close (), read ( 1 write ( ) functions analogous to a device, open, close, read and‏
‎nctions. The BSD Unix interface differs slightly from Unix ۱‏ 0
‎gis are two types of file systems. ۱‏
‎Block file യയ Its lige 0 generates records to be saved into the memory. These are first structured‏ .|
‎jnto a suitable format and then translated into block streams. A file pointer (record) points to a block‏

‎from the start to the end of the file.

‎2, Byte stream file system. \ts application generates record streams. These streams are to be saved into
the memory. These are first structured into a suitable format and then translated into byte streams. A
file pointer (byte index) points to a byte from the start index = 0 to ‏مز احلا‎ file of N bytes.

‎1051 85 each process has a | descriptor (PCB); a file system has a data structure, called file descriptor
8.9). The structure differs from one file manager to another, File descriptor, fd, for a file is an integer,
which returns on opening a file. fd points to the data structure of the file. fd is usable till the closing of the file.

‎Table 8.9 Data Structure of File Descriptor in a Typical File System

‎−−−
‎⋒ Descriptor Meaning(s)

‎Identity Name by which a file is identified in the application

‎Creator or owner Process or program by which it was created

‎State A state can be ‘closed’ , ‘archived’ (saved), ‘open executing file’ or ‘open file for additions’

‎Locks and protection fields O_RDWR file opens with read and write permissions, O_RDONLY file opens with
read only permissions, O_WRONLY file opens with write only permissions

‎File info Current length, when created, when last modified, when last accessed

‎Sharing permission Can be shared for execution, reading or writing

‎Count Number of directories referring to it
Storing media details Blocks transferable per access

‎A file manager creates, opens, reads, seeks a record, writes and closes a file. A file has a file descriptor.

‎8.6.3 1/೦ Subsystems

‎⋅ systems. Drivers communicate with th ∙
VO ports are stems of OS device management systems ^ 3 00
that use ടു + ‏سد ےی‎ depend on the hardware ऋषी 1/0 systems differ in different OSes.
iven in Table 8.10.
Subsyste ‘cal 10 system are as given In able

‎y ० (சை of 10 operations-synchronous and asynchronous. There may be separate functions for
Synchronous and synchronous operations in an RTOS. In case of traditional OS, only synchronous 105 may

‎Supported. न 0 ۱
ടിയില്‍ 0 operations are at certain ixed data ‏سرد‎ see ಇ, a task (process) blocks tills
till completion of the 1௦ For example, a write function, write () for ta transfer to a buffer. Synchronous

‎: வடட the data transfer will block the task till 1
∙ ம்‌ 2 ous 10 initiates, ! ४ ॥ kB data gets
tansferred t the buffer. பயல்கள்‌ () once initiated blocks the task till | KB is read.